U.S. patent number 10,775,283 [Application Number 16/189,192] was granted by the patent office on 2020-09-15 for on-demand vapor generator.
This patent grant is currently assigned to SMITHS DETECTION-WATFORD LIMITED. The grantee listed for this patent is SMITHS DETECTION-WATFORD LIMITED. Invention is credited to Jonathan Atkinson, John Fitzgerald, Marcedl Gowers, Alexander Parker.
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United States Patent |
10,775,283 |
Parker , et al. |
September 15, 2020 |
On-demand vapor generator
Abstract
An on-demand vapour generator includes a vapour chamber
configured to produce a vapour and a vapour absorption assembly
configured to receive flows of vapour from the vapour chamber. The
vapour absorption assembly includes a first vapour-permeable
passage having a passage outlet and at least one second
vapour-permeable passage that is closed. When vapour absorption
assembly receives a flow of vapour from the vapour chamber, the
flow of vapour passes through the first vapour-permeable passage to
the passage outlet at least substantially without absorption of
vapour from the flow of vapour. However, when a flow of vapour is
not received from the vapour chamber, vapour entering the vapour
absorption assembly from the vapour chamber passes into the first
vapour-permeable passage and the at least one second
vapour-permeable passage and is at least substantially
absorbed.
Inventors: |
Parker; Alexander (Hemel
Hempstead, GB), Gowers; Marcedl (Hertfordshire,
GB), Atkinson; Jonathan (Herts, GB),
Fitzgerald; John (Watford, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
SMITHS DETECTION-WATFORD LIMITED |
Hertfordshire |
N/A |
GB |
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Assignee: |
SMITHS DETECTION-WATFORD
LIMITED (Hertfordshire, GB)
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Family
ID: |
49552386 |
Appl.
No.: |
16/189,192 |
Filed: |
November 13, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190086304 A1 |
Mar 21, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15609343 |
May 31, 2017 |
10126217 |
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14430252 |
Jul 18, 2017 |
9709470 |
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PCT/GB2013/052498 |
Sep 24, 2013 |
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61705068 |
Sep 24, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F22B
3/02 (20130101); G01N 1/38 (20130101); B01D
53/229 (20130101); B01B 1/005 (20130101); B01L
3/0289 (20130101); G01N 27/622 (20130101) |
Current International
Class: |
H01J
49/00 (20060101); B01B 1/00 (20060101); F22B
3/02 (20060101); B01D 53/22 (20060101); B01L
3/02 (20060101); G01N 1/38 (20060101); G01N
27/62 (20060101) |
Field of
Search: |
;250/281,282,288 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101583867 |
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Nov 2009 |
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CN |
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101939641 |
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Jan 2011 |
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CN |
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2009513950 |
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Apr 2009 |
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JP |
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2265832 |
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Dec 2005 |
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RU |
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Other References
International Search Report for PCT/GB2013/052498 dated Dec. 18,
2013. cited by applicant .
Office Action dated Mar. 18, 2016 for Chinese Appln. No.
201380049735.7. cited by applicant .
Office Action dated Jun. 6, 2017 for Japenese Appln. No.
2015-532510. cited by applicant .
Office Action dated Sep. 12, 2017 for Russian Appln. No.
2015109722/05. cited by applicant.
|
Primary Examiner: McCormack; Jason L
Attorney, Agent or Firm: West; Kevin E. Advent, LLP
Claims
What is claimed is:
1. A vapour generator comprising: a vapour chamber configured to
produce a vapour; and a vapour absorption assembly including a
first vapour-permeable passage having a passage outlet, at least
one second vapour-permeable passage, and a passage inlet configured
to receive flows of vapour from the vapour chamber, the first
vapour-permeable passage having a first end in fluid communication
with the passage inlet and a second end in fluid communication with
the passage outlet, the vapour absorption assembly configured to
receive flows of vapour from the vapour chamber via the passage
inlet, the at least one second vapour-permeable passage fluidly
coupled with the first vapour-permeable passage, wherein when a
flow of vapour driven from the vapour chamber is received, the flow
of vapour passes from the passage inlet through the first
vapour-permeable passage to the passage outlet at least
substantially without absorption of vapour from the flow of vapour
and without being substantially diverted to the at least one second
vapour-permeable passage, and when a driven flow of vapour is not
received from the vapour chamber, vapour entering the vapour
absorption assembly from the vapour chamber passes into the first
vapour-permeable passage and into the at least one second
vapour-permeable passage, the at least one second vapour-permeable
passage configured to take up the vapour, the first vapour
permeable passage and the at least one second vapour-permeable
passage arranged so that, in response to a pressure difference
between the outlet and the vapour source, resistance to driving
vapour flow through the first vapour permeable passage to the
outlet is less than the resistance to driving vapour flow into the
at least one second vapour-permeable passage.
2. The vapour generator of claim 1, wherein the at least one second
vapour-permeable passage comprises a dead volume.
3. The vapour generator of claim 1, wherein the at least one second
vapour-permeable passage defines a sink separated from the outlet
by the first vapour permeable passage.
4. The vapour generator of claim 3, wherein the sink comprises a
material adapted to take up the vapour and is arranged to divert
diffusion of vapour away from the passage outlet.
5. The vapour generator of claim 1, wherein the at least one second
vapour-permeable passage comprises a material adapted to take up
the vapour.
6. The vapour generator of claim 5, wherein the take up of vapour
comprises absorption.
7. The vapour generator of claim 6, wherein the absorption
comprises at least one of adsorbing the vapour onto a surface,
chemical absorption, take up of the vapour by chemical or molecular
action, and at least temporary capture of the vapour in a porous
material.
8. The vapour generator of claim 1, wherein the vapour absorption
assembly defines an impeder, the vapour chamber configured to be a
vapour source.
Description
BACKGROUND
Ion mobility spectrometry (IMS) refers to an analytical technique
that can be used to separate and identify ionized material, such as
molecules and atoms. Ionized material can be identified in the gas
phase based on mobility in a carrier buffer gas. Thus, an ion
mobility spectrometer (IMS) can identify material from a sample of
interest by ionizing the material and measuring the time it takes
the resulting ions to reach a detector. An ion's time of flight is
associated with its ion mobility, which relates to the mass and
geometry of the material that was ionized. The output of an IMS
detector can be visually represented as a spectrum of peak height
versus drift time.
IMS detectors and other detectors often include a vapour generator
to supply a dopant chemical to the detector. Vapour generators can
also be used to supply a test chemical for use in testing or
calibrating a detector, a filter or other equipment. In some
applications it is important that the vapour generator can be
switched on and off rapidly, and that leakage can be prevented when
the detector is switched off. For example, in an IMS detection
system, rapid switching of the vapour generator on and off enables
rapid switching between different doping conditions, such as
different levels of dopant or different dopant substances. Such
rapid switching could also enable different regions of the IMS
detector to be doped differently by ensuring there was no leakage
to undoped regions of the apparatus when the apparatus is switched
off.
SUMMARY
An On-Demand Vapour Generator (OVG) is disclosed. The vapour
generator may be configured for use with a detection apparatus,
such vapour generators may comprise a vapour source coupled by a
flow path to provide vapour through an impeder to an outlet for
dispensing vapour to the detection apparatus. The impeder may
comprise: a first vapour permeable passage arranged to impede
diffusion of the vapour from the source to the owlet. The vapour
permeable passage is configured to enable vapour to be driven
through a diffusion barrier from the source to the outlet by a
pressure difference (e.g. pumped or forced flow as opposed to
simply a difference in concentration). The vapour generator may
also comprise at least one additional vapour permeable passage to
act as a sink, coupled to the outlet by the first vapour permeable
passage. The sink can comprise a material adapted to take up the
vapour to divert diffusion of vapour away from the outlet. In
embodiments, the first vapour permeable passage and the sink are
arranged so in response to a pressure difference between the outlet
and the vapour source, resistance to driving vapour flow through
the first vapour permeable passage to the outlet is less than the
resistance to driving vapour flow into the sink. In one or more
implementations, the vapour generator includes a vapour chamber
configured to produce a vapour and a vapour absorption assembly
configured to receive flows of vapour from the vapour chamber, for
example via a diffusion barrier. The vapour absorption assembly
includes a first vapour-permeable passage having a passage outlet.
The vapour absorption assembly may further include one or more
second vapour-permeable passages that are closed. When the vapour
absorption assembly receives a flow (e.g. a pressure driven flow)
of vapour from the vapour chamber, the flow of vapour passes
through the first vapour-permeable passage to the passage outlet at
least substantially without absorption of vapour from the flow of
vapour. However, when a flow of vapour is not received from the
vapour chamber, vapour entering the vapour absorption assembly from
the vapour chamber passes into the first vapour-permeable passage
and the at least one second vapour-permeable passage and is at
least substantially absorbed.
This Summary is provided to introduce a selection of concepts in a
simplified form that are further described below in the Detailed
Description. This Summary is not intended to identify key features
or essential features of the claimed subject matter, nor is it
intended to be used as an aid in determining the scope of the
claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
The detailed description is described with reference to the
accompanying figures. In the figures, the left-most digit(s) of a
reference number identify the figure in which the reference number
first appears. The use of the same reference number in different
instances in the description and the figures may indicate similar
or identical items.
FIG. 1 is a schematic block diagram that illustrates an example
on-demand vapour generator in accordance with an implementation of
the disclosure, wherein the on-demand vapour generator employs a
single vapour-permeable passage.
FIG. 2 is a schematic block diagram that illustrates another
example on-demand vapour generator in accordance with an
implementation of the disclosure, wherein the on-demand vapour
generator employs a single vapour-permeable passage.
FIG. 3 is a schematic block diagram that illustrates an example
on-demand vapour generator in accordance with an implementation of
the disclosure, wherein the on-demand vapour generator employs a
vapour-permeable passage having a passage outlet and one or more
vapour-permeable passages that are closed.
FIG. 4 is a schematic block diagram that illustrates an example
on-demand vapour generator in accordance with another
implementation of the disclosure, wherein the on-demand vapour
generator employs a vapour-permeable passage having a passage
outlet and one or more vapour-permeable passages that are
closed.
DETAILED DESCRIPTION
One technique of reducing leakage of vapour from a vapour generator
when the vapour generator is turned off employs a container of
absorbent material that is connected an outlet of a vapour
generator via a T-junction. When the generator is turned on, the
gas flow through the vapour generator rises to a level that is
sufficient to ensure that most of the vapour is carried through the
other arm of the T-junction to the outlet. When the vapour
generator is off and there is a nominal (e.g., zero (0)) flow, some
of the residual vapour produced passes via one arm of the
T-junction to the absorbent material. However, some vapour may
bypass the absorbent material leading to relatively low absorption
efficiency and relatively high levels of escaped vapour.
An on-demand vapour generator is disclosed that is suitable for use
in a detection system such as an IMS detection system, a gas
chromatograph system, a mass spectrometer system, and so forth, to
supply a flow of vapour to a detector apparatus (e.g., an IMS
detector, a gas chromatograph, a mass spectrometer, and so forth)
of the system. In one or more implementations, the vapour generator
includes a vapour chamber configured to produce a vapour. The
vapour chamber includes a vapour chamber inlet configured to
receive a flow of gas into the vapour chamber to generate a flow of
vapour, and a vapour chamber outlet configured to allow the flow of
vapour to exit the vapour chamber. A vapour absorption assembly
receives flows of vapour from the vapour chamber and ports them to
the detection apparatus (e.g., to an IMS detector). The vapour
absorption assembly includes a vapour-absorbent material configured
to absorb the vapour produced by the vapour chamber. A
vapour-permeable passage having a passage outlet extends through
the vapour-absorbent material and is coupled to the detector
assembly. The vapour absorption assembly may further include at
least one additional vapour-permeable passage that is closed (e.g.,
blocked so as to form a "dead end" vapour-permeable passage). When
a flow of vapour is not driven (e.g. pumped or drawn) from the
vapour chamber (e.g., the on-demand vapour generator is turned off
so that there is negligible or no flow), any vapour entering the
vapour absorption assembly from the vapour chamber passes into the
vapour-permeable passage having the passage outlet and/or the one
or more additional dead end vapour-permeable passages and is at
least substantially absorbed by the vapour absorbing material. When
the vapour absorption assembly receives a flow of vapour (e.g. when
the flow of vapour is pumped or drawn) from the vapour chamber, the
flow of vapour passes through the first vapour-permeable passage to
the passage outlet. As the flow is driven through the passage, more
vapour passes to the outlet without being absorbed than when the
flow is not driven.
FIGS. 1 through 4 illustrate on-demand vapour generators 100 in
accordance with example implementations of the present disclosure.
As shown, the vapour generator 100 includes an inlet 102 and a
vapour outlet 103 connected to an inlet of a detector apparatus
104. The vapour generator 100 is configured to furnish a readily
controllable supply of a dopant vapour to the detector apparatus
104. In implementations, the vapour generator 100 may supply a flow
of vapour to a variety of detector apparatus. For example, in one
implementation, the detector apparatus 104 may comprise an IMS
detector. However, the vapour generator 100 can be used in
conjunction with other detectors such as gas chromatography
instruments, and so forth. The vapour generator 100 may also be
used for calibration purposes within the instrument. In
implementations, the vapour generator 100 and detector apparatus
104 may be part of a detection system (e.g., an IMS detection
system) 10. In such detection systems 10, the vapour generator 100
and the detector assembly can be housed within a common
housing.
The vapour generator 100 includes a gas (e.g., air) flow generator
106 such as a fan, a blower, a compressed gas source, and so forth.
The flow generator 106 is configured to be switched on or off to
provide a flow of gas (air) to its outlet 107 as desired. The flow
generator 106 may include various filters or other devices to
remove contaminants and water vapour form the gas (e.g., from
atmospheric air) before the gas is supplied to the outlet 107.
The outlet 107 of the flow generator 106 is in fluid communication
with (e.g., is coupled to) an inlet 108 at one end of a vapour
chamber 109. The vapour chamber 109 may have a variety of
configurations, and may comprise any kind of vapour source, for
example a permeation source, for example a diffusion source. For
example, in the implementation shown, the vapour chamber 109
includes a housing 110 that contains a wicking, absorbent material
111 saturated with a compound in its liquid phase so that the space
of the interior 112 within the housing I 10 above the absorbent
material 111 is at least substantially filled with a vapour of the
liquid at the liquid's saturated vapour pressure at ambient
temperature. The vapour chamber 109 includes an outlet 113 at the
end opposite the inlet 108 through which a flow of vapour,
comprised of the vapour and gas, can flow out of the vapour chamber
109. In implementations, the vapour producing liquid comprises
acetone. However, vapour-producing substances other than acetone
can be used.
The vapour chamber outlet 113 is in fluid communication with (e.g.,
is coupled to) an inlet 114 of a vapour absorption assembly 115,
for example via a diffusion barrier. The vapour absorption assembly
115 includes a vapour absorbent 116 configured to absorb the vapour
produced by the vapour chamber 109. A vapour-permeable passage
(main flow path) 117 having an outlet (vapour outlet 103) extends
through the vapour absorbent 116 and is coupled to the detector
apparatus 104. In the illustrated implementations, the vapour
absorption assembly 115 includes a single vapour-permeable passage
117. However, it is contemplated that additional vapour-permeable
passages 117 may be provided in parallel to the passage 117 shown.
Moreover, a second vapour absorption assembly can be provided
between the inlet 108 of the vapour chamber 109 and the flow
generator 106 to prevent vapour from the chamber 109 passing to the
flow generator 106 in significant quantities when the flow of gas
is off (e.g., when the flow generator 106 is turned off). A
pneumatic valve can be connected between this second vapour
absorption assembly and the vapour chamber. This valve may be
maintained closed until gas (air) flow is required.
The on demand vapour generator 100 may further include one or more
diffusion barriers 105. In implementations, the diffusion barriers
may comprise flow paths with a small cross sectional area that
limit the rate of diffusion (and therefore loss) of vapour from the
vapour generator 100 when the generator 100 is in the off state
(e.g., when no flow of vapour is furnished by the vapour generator
100).
When the vapour generator 100 is off (e.g., is in the "off" state,
that is, when no flow of vapour is provided), the flow generator
106 remains off so that there is no flow of gas (air) through the
vapour chamber 109 and the vapour-permeable passage 117. The
vapour-permeable passage 117 is open to the interior 112 of the
vapour chamber 109 so that some vapour may drift into the passage
117. As this drift occurs, the vapour diffuses into the
vapour-absorbent material and is absorbed therein. The bore,
length, porosity and nature of the vapour absorbent 116 are chosen
such that, under zero flow conditions (e.g., no or virtually no
flow conditions), the amount of vapour that escapes from the outlet
103 end of the passage 117 is insignificant in the context of the
application in which the vapour generator 100 is used. For example,
where the vapour generator 100 is used as a dopant source in an TMS
detector, the vapour dopant flow in the off state is arranged to be
not sufficient to produce any noticeable dopant ion peak by the IMS
detector.
The vapour generator 100 is turned on to produce a flow of vapour
at its outlet 103 by turning on the flow generator 106 to produce a
flow of gas (air) into the inlet 108 of the vapour chamber 109.
This flow of gas (air) collects the vapour produced in the vapour
chamber 109 and pushes it through the outlet 113 and into the
passage 117 of the vapour absorption assembly 115. The flow
velocity in the passage 117 is chosen such that the residence time
of the collected vapour in the passage is sufficiently low so that
little vapour is absorbed into the vapour absorbent 116. Thus, a
greater proportion of the vapour passes through the
vapour-permeable passage 117 to the outlet 103 end of the passage
117 to be delivered to the detector apparatus 104 than when the
flow generator is off The flow of vapour can be continuous or
pulsed.
The vapour generator 100 is configured to be capable of turning off
vapour flow very rapidly when not required, such that the vapour
does not leak out at a significant rate. In an IMS detection
system, this effectively prevents dopant vapour from entering the
IMS detector when the system is turned off and is not powered. This
can also enable selected regions of IMS detector to be doped with a
reduced risk that dopant will leak to undoped regions when the
apparatus is turned off In conventional systems, gas flow through
the IMS detector can keep undoped regions free of dopant when the
apparatus is powered but, when not powered, the gas flow ceases and
any slight leakage of dopant will contaminate all regions of the
apparatus. This has previously made it very difficult to dope
different regions of IMS detector differently except where the
apparatus is continuously powered.
In FIGS. 1 through 4, the flow generator 106 is illustrated as
being in fluid communication with (e.g., connected to) the inlet
102 of the vapour chamber 109 to push air into the chamber 109.
However, in other implementations, the flow generator 106 may be
connected downstream of the vapour chamber 109 and be arranged to
pull air into the chamber 109. For example, the flow generator 106
may be connected between the outlet 113 of the vapour chamber 109
and the inlet 114 of the vapour absorption assembly 115 (the inlet
114 end of the vapour-permeable passage 117), or it could be
connected downstream of the vapour absorption assembly 115 (at the
outlet 103 end of the passage 117).
In the implementations shown in FIGS. 3 and 4, the vapour
absorption assembly 115 is illustrated as further including one or
more additional vapour-permeable passages (region) that are closed
(e.g., blocked) so as to form "dead end" vapour-permeable passages
(four (4) dead end vapour-permeable passages 317A-D, collectively
317, are illustrated). As shown, the dead end vapour-permeable
passages 317 may thus extend only partially through the vapour
absorbent 116, and do not include outlets.
When the vapour absorption assembly 115 receives a flow of vapour
from the vapour chamber 109 (e.g., the flow generator 106 is turn
on), the flow of vapour passes through the primary vapour-permeable
passage 117, which functions as a main flow path, to the passage
outlet 103 at least substantially without absorption of vapour from
the flow of vapour by the vapour absorbent 116. However, when a
flow of vapour is not received from the vapour chamber (e.g., the
flow generator 106 is turned off so that there is negligible or no
flow of vapour), vapour entering the vapour absorption assembly 115
from the vapour chamber 109 passes into the vapour-permeable
passage 117 and/or the dead end vapour-permeable passages 317 and
is at least substantially absorbed by the vapour absorbent 116.
When the vapour generator 100 is in the off-state (e.g., when no
flow of vapour is supplied), vapour diffusing out of the vapour
chamber 109 enters the vapour absorption assembly 115 as before,
but now passes down both the vapour-permeable passage 117 (main
flow path) and the dead end vapour-permeable passages 317. As a
result, the area of absorption provided f.COPYRGT.r the vapour (and
therefore the extent of absorption) is greatly increased. However,
when the vapour generator 100 is in the on-state (e.g., when a flow
of vapour is supplied), the dead end vapour-permeable passages 317
act as dead volumes with essentially no gas exchange and do not
contribute to the absorption of vapour from the flow of vapour.
Therefore, there is no significant change in the concentration of
vapour exiting the vapour generator 100 with the the dead end
vapour-permeable passages 317 from implementations that include
only the vapour-permeable passage 117 without the dead end
vapour-permeable passages 317.
In implementations, the addition of dead-end vapour-permeable
passages 317 allows the width of the temperature range over which
the on-demand vapour generator 100 can be operated to be increased.
As temperature increases, the activity of permeation and diffusion
sources rise, the rate of diffusion rises, and the ability of
absorbent materials (e.g. activated charcoal) to capture chemicals
often decreases. Consequently, a greater concentration of vapour,
at a higher rate, is delivered to the vapour absorption assembly
115 of the vapour generator 100. This increase will be compounded
by the reduction in absorption capacity/rate, leading to the vapour
absorption assembly 115 being less capable of dealing with the
vapour. Leakage in the off-state may therefore increase. Therefore,
when the vapour-permeable passage 117 of the vapour absorption
assemblies 115 shown in FIGS. 1 and 2 (without dead end
vapour-permeable passages 317) are designed to be of suitable
length to allow an adequate concentration of vapour to exit the
vapour generator 100 in the on-state at extremely low temperatures,
the passages 117 may not be adequately long to absorb all vapour in
the off-state at extremely high temperatures. The addition of dead
end vapour-permeable passages 317 to the vapour absorption assembly
115, as shown in FIGS. 3 and 4, increases the off-state absorption
while not decreasing the on-state vapour concentration exiting the
vapour generator 100. Accordingly, the addition of dead end
vapour-permeable passages 317 to the vapour absorption assembly 115
makes it possible to reduce the leakage of vapour over a greater
range of temperatures without limiting the ability of the vapour
generator 100 to supply adequate vapour at extremely low
temperatures. Moreover, the additions of dead end vapour-permeable
passages 317 makes it possible to further increase the
concentration of the vapour leaving the vapour generator 100
without compromising the ability of the vapour generator 100 to
restrict the leakage of vapour in the off-state.
In implementations, addition of dead end vapour-permeable passages
317 to the vapour absorption assembly 115, as shown in FIGS. 3 and
4, may facilitate shortening of the main flow path (e.g.,
shortening of the vapour-permeable passage 117) to allow higher
vapour concentrations to be produced by the vapour generator 100 in
the on-state without limiting the ability of the generator 100 to
limit leakage in the off-state. Moreover, in situations where the
detection system 10 is to be operated over a range of temperatures,
the addition of dead end vapour-permeable passages 317 to the
vapour absorption assembly 115 enhances the ability of the vapour
generator 100 to furnish an adequate concentration of vapour
exiting the vapour generator 100 in the on-state at low temperature
by having a short main flow path (when the activity of the source
is lower than at high temperature), while simultaneously
restricting the leakage of the vapour generator 100 in the
off-state to acceptable levels at higher temperatures (when the
activity of the source and the rate of diffusion are higher than at
low temperatures),
The dimensions, layout and configuration of the vapour absorption
assemblies 115 of the on-demand vapour generators 100 shown in
FIGS. 1 through 4, including the the vapour-permeable passage 117
(main flow path) and/or the dead end vapour-permeable passages 317
may vary depending on a variety of factors including, but not
limited to: the activity of the vapour source (vapour chamber 109),
the required concentrations to be provided, the flows used in the
on-state of the vapour generator 100, the acceptable level of
release when in the off-state and the conditions (e.g. temperature)
under which the vapour generator 100 be operated. Accordingly, any
dimensions, layouts, or configurations presented herein are for
illustrative purposes, and are not necessarily meant to be
restrictive of the disclosure.
In implementations shown in FIGS. 1 and 3, the vapour-permeable
passage 117 and/or the dead end vapour-permeable passages 317 of
the vapour absorption assembly 115 comprise machined bores formed
in a block 118 of an absorbent material such as carbon (e.g.,
activated charcoal) or a sintered material, such as a molecular
sieve material, which could be of zeolite. In other
implementations, the vapour-permeable passage 117 and dead end
vapour-permeable passages 317 may be formed by molding the block
118 about a core structure that is subsequently removed. The
absorbent material is configured to be absorbent of the vapour
(e.g., of acetone vapour, and so forth). For example, the material
may itself be formed of an absorbent material, such as carbon
(e.g., activated charcoal), or the material itself may be a
non-absorbent material rendered absorbent via impregnation with a
suitable substance. In this manner, the vapour (e.g., acetone
vapour, and so forth) may be absorbed by the vapour absorbent 116
generally along the length of the vapour-permeable passage 117 and
within the dead-end vapour-permeable passages.
In the implementation shown in FIGS. 2 and 4, the vapour-permeable
passage 117 and/or the dead end vapour-permeable passages 317
comprise lengths of tube 219 having a vapour-permeable outer wall
or membrane 220 that are at least substantially enclosed within an
outer housing 221 formed of a vapour-impermeable material. For
example, as shown, the tube 219 forming, the vapour-permeable
passage 117 may extend axially along the center of the housing 221,
while tubes 219 forming the dead end vapour-permeable passages 317
are arrayed around the central tube. As shown, the tube 219 that
forms the vapour-permeable passage 117 includes a first end coupled
to the inlet 114 and a second end coupled to the vapour outlet 103.
Similarly, the tubes that form the dead end vapour-permeable
passages 317 include first ends that are coupled to the inlet 114.
However, the second ends of these tubes are blocked and do not
extend from the housing 221. The bore, length, wall thickness and
material of the tubes 219 may be chosen such that, under zero flow
conditions, the amount of vapour that escapes from the outlet 103
end of the tube 219 is insignificant in the context of the
application in which the vapour generator 100 is employed. In one
example, the tube 219 forming the vapour-permeable passage 117
shown in FIG. 2 is approximately one hundred millimeters (100 mm)
long with an external diameter of approximately one millimeter (1
mm), and an internal diameter of approximately one half millimeter
(0.5 mm). However, tubes 219 having other sizes are contemplated.
The volume between the outside surface of the tubes 219 and the
inside surface of the housing 221 is at least substantially Filled
with a material 221 that readily absorbs the vapour produced by the
vapour chamber 109. In implementations, the material 221 may
comprise activated charcoal granules that are effective to absorb
vapour, such as acetone vapour, or the like. Thus, the tubes 219
may be surrounded on all sides by the absorbent charcoal granules.
In implementations, the tubes 219 may be formed of an elastomeric
plastic, such as silicone rubber, and so forth.
In implementations, the on-demand vapour generator 100 may further
include a pneumatic valve connected to block flow of vapour from
the vapour chamber 109 to the absorbent passage until vapour flow
is employed. The pneumatic valve would have the advantage of
preventing continual adsorption of the vapour into the vapour
absorbent 116, thus lengthening the life of both the vapour chamber
109 and the absorbent material of the vapour absorbent 116. The
vapour-permeable passage 117 and/or the dead end vapour-permeable
passages 317 may thus trap vapour that permeates through the valve
seals, providing a lower rate of diffusion. Consequently, the size
of the vapour absorbent assembly 115 (e.g., the length, surface
area, etc. of the vapour-permeable passage 117 and/or the dead end
vapour-permeable passages 317) may be reduced.
In FIGS. 1 through 4, the vapour absorbent 116 is illustrated as
extending around the vapour-permeable passage 117 and/or the dead
end vapour-permeable passages 317. However, in implementations, the
entire vapour generator 100 may be at least substantially enclosed
in a vapour absorbent so that vapour does not substantially escape
from the vapour generator 100 in the off state.
The on-demand vapour generator 100 of the present disclosure
provides for efficient trapping of vapour. The vapour generator 100
is not confined to use in doping detectors but could be used in
other applications. For example, the vapour generator 100 may be
used to provide a periodic internal calibrant material in a
detection system 10. The detection system 10 may be an IMS
detection system, gas chromatograph system, a mass spectrometer or
other system. The vapour generator 100 may be used for calibration
or testing of other detectors, filters, and so forth.
As will be appreciated in the context of the present disclosure,
the vapour generator need not generate new vapour, it may generate
pre-existing vapour obtained from a vapour source, e.g. a reservoir
of vapour. As will also be appreciated in the context of the
present disclosure, the term "absorption" need not imply chemical
or molecular action, and may be taken to comprise at least one of
adsorbing the vapour onto a surface, chemical absorption, take up
of the vapour by chemical or molecular action, and at least
temporary capture of the vapour in a porous material. As will also
be appreciated, the volume flow rate along a flow passage may
depend on the length and cross section of the flow passage, and the
pressure difference applied to drive flow along the passage.
Accordingly, a vapour permeable passage provides an example of a
flow impeder in that the volume flow rate along the passage is
impeded by the finite cross section and finite width of the
passage. Flow may also be impeded by other examples of flow
impeders such as any means of inhibiting flow, for example by
slowing flow by means of adsorption, absorption, or by interposing
a barrier in the flow.
Although the subject matter has been described in language specific
to structural features and/or methodological acts, it is to be
understood that the subject matter defined in the appended claims
is not necessarily limited to the specific features or acts
described. Although various configurations are discussed the
apparatus, systems, subsystems, components, and so forth can be
constructed in a variety of ways without departing from this
disclosure. Rather, the specific features and acts are disclosed as
example forms of implementing the claims.
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